Intervening earlier to improve brain health might help you stay sharper as you age. The fight against dementia actually starts in your 40s. Midlife, not your 70s or 80s, is when brain changes start to occur that can pave the way toward dementia 🧠, Alzheimer’s disease and cognitive decline later, according to a growing body of research. Intervening earlier to improve brain health might help people stay sharper in their later years.